1. Field of the Invention
The present invention relates to a method for producing a magnetic recording medium, in particular, a producing method of a magnetic recording medium which is excellent in surface properties and capable of achieving high output.
2. Description of the Related Art
With the trend of the increase of density of magnetic recording media in recent years, recording wavelength has become narrow. As a result, the thickness of a magnetic layer has become thinner. On the other hand, separately from main recording, tracking signal recording such as servo signals has become necessary. Therefore, a multilayer magnetic recording medium having a plurality of magnetic recording layers has been proposed. As producing methods and producing apparatuses therefor, e.g., JP-A-5-212337 (the term "JP-A" as used herein means an "Unexamined Japanese patent Publication (kokai)") suggests simultaneous multilayer coating methods and apparatuses.
The techniques disclosed in JP-A-5-212337 has elaborated to discharge a coating solution from a plurality of slits for effectively preventing generation of uneven colors and vertical streaks in multilayer coating of thin layers, and preventing the reduction of orientation properties to manufacture good magnetic recording media stably. Further, at least a coating solution for the lowermost layer is made nonmagnetic solution and a coating unit the edge shape of which is contrived is used for coating.
However, in such a multilayer simultaneous coating method, it is very difficult to select optimal viscosity of a coating solution of each layer to obtain a desired coating thickness of each layer while preventing the turbulence in the interface between each layer, at the same time, ensuring the surface properties of the uppermost layer. Further, a coating unit becomes complicated because at least three feeding pipe and slits are required. In addition, when a magnetic recording medium comprises a plurality of magnetic layers, control and insurance of the thickness of each layer during production are difficult.